The process used for injection molding is the injection molding process, which requires the use of professional injection molding machines to mold the material. The important conditions that affect the injection molding process include the temperature of plasticizing flow and cooling, pressure and the corresponding individual action time.
The injection molding process needs to control the temperature of the barrel, nozzle temperature and mold temperature. The first two temperatures mainly affect the plasticization and flow of plastic, while the latter temperature mainly affects the flow and cooling of plastic. Each kind of plastic has different flow temperature, the same kind of plastic, due to different sources or grades, its flow temperature and decomposition temperature is different, which is due to different average molecular weight and molecular weight distribution, plastic plasticization process in different types of injection machines is also different, so the choice of barrel temperature is also different.
Nozzle temperature is usually slightly lower than the maximum temperature of the barrel, which is to prevent the melt in the straight-through nozzle may occur "salivation phenomenon". Nozzle temperature can not be too low, otherwise it will cause the early condensation of the melt and the nozzle blocked, or due to early condensation of the material into the cavity and affect the performance of the product.
Mold temperature has a great influence on the intrinsic performance and apparent quality of the products. The temperature of the mold is determined by the crystallinity of the plastic, the size and structure of the product, performance requirements, and other process conditions: melt temperature, injection speed and injection pressure, molding cycle, etc.
The pressure in the injection molding process includes plasticizing pressure and injection pressure, and directly affects the plasticization of plastic and the quality of products.
When using screw injection machine, the top of the screw melt in the screw rotation back pressure is called plasticizing pressure, also known as back pressure. The size of this pressure can be adjusted by the relief valve in the hydraulic system. In injection, the magnitude of the plasticizing pressure is constant with the rotational speed of the screw, so increasing the plasticizing pressure will increase the temperature of the melt, but will reduce the rate of plasticization. In addition, increasing the plasticizing pressure often leads to uniform temperature of the melt, uniform mixing of the color and discharge of gas from the melt. In general operation, the decision of plasticizing pressure should be in the premise of ensuring the excellent quality of products, the lower the better, the specific value is different with the variety of plastic used.
In current production, the injection pressure of almost all injection machines is based on the pressure applied to the plastic by the top of the plunger or screw (converted from the oil circuit pressure). The role of injection pressure in injection molding technology is to overcome the resistance to the flow of plastic from the barrel to the cavity, to give the rate of molten material filling the mold and to compact the molten material.